1. Psyc 552 Ergonomics & Biomechanics Lecture 14

2. Evaluating Lifting with NIOSH  National Institute of Occupational Health & Safety.  Created Lifting Equation in 1994.  The multiplicative model that computes a Lifting Index (LI).  LIs > 1.0 pose greater risk of low back pain.

3. NIOSH Equation Components Vertical location Horizontal location Load weight Container characteristics

4. NIOSH Equation Components Asymmetry angle Other Task Measures  Frequency of lifts  Lifting duration

5. Components to Multipliers  RWL = Recommended Weight Limit  LC = Load Constant (51 lbs)  HM = Horizontal Multiplier  VM = Vertical Multiplier  DM = Distance Multiplier  AM = Asymmetry Multiplier  FM = Frequency Multiplier  CM = Coupling Multiplier RWL = LC x HM x VM x DM x AM x FM x CM

6. Variables – Horizontal Component  Horizontal Location (H) is measured from the mid- point of the line joining the inner ankle bones to a point projected on the floor directly below the mid- point of the hand grasps (i.e., load center), as defined by the large middle knuckle of the hand.  H = 8 + W/2 for V => 10 inches  H = 10 + W/2 for V < 10 inches  W = width of the container in the sagittal plane and V is the vertical location of the hands from the floor.

7. Variables – Horizontal Multiplier  HM = 10/H  When H < 10, HM = 1  When H >25”, HM = 0

8. Variables – Vertical Component  The vertical location should be measured at the origin and the destination of the lift to determine the travel distance (D)

9. Variables – Vertical Multiplier  VM is based on the absolute deviation of V from the optimal or knuckle height of an average worker.  VM = 1(.0075|V-30|) – for inches  When V is at 30 inches (75 cm), the vertical multiplier (VM) is 1.0.  If V is greater than 70 inches, then VM = 0

10. Variables – Distance Component  Vertical Travel Distance variable (D) is defined as the vertical travel distance of the hands between the origin and destination of the lift.  DM = (.82 + (1.8/D)) – for inches  The DM is 1.0 when D is set at 10 inches; DM is 0.85 when D = 70 inches

11. Variables – Asymmetry Component  Asymmetric angle (A) defined as the angle between the asymmetry line and the mid- sagittal line. The asymmetry line is the horizontal line that joins the mid-point between the inner ankle bones and the point projected on the floor directly below the mid- point of the hand grasps, as defined by the large middle knuckle.

12. Variables – Asymmetry Component  The asymmetry angle (A) must always be measured at the origin of the lift. If significant control is required at the destination, however, then angle A should be measured at both the origin and the destination of the lift.

13. Variables – Asymmetry Multiplier  AM = 1-(.0032A)  The range is from a value of 0.57 at 135 degrees of asymmetry to a value of 1.0 at 0 degrees of asymmetry.  If A is greater than 135 degrees, then AM = 0

14. Variables – Frequency Component  Frequency is: The number of lifts per minute (F) The amount of time engaged in lifting (duration) The vertical height of the lift from the floor.

15.  Lifting frequency is the average number of lifts per minute over a 15 minute period.  When work does not require lifting for 15 minutes and the lifting frequency does not exceed 15 lifts per minute then: Compute the total number of lifts for a 15 minute period – (lift rate X work time) Divide the total number of lifts by 15 Use the quotient as the frequency F for the table. Frequency Special Considerations

16. Lifting Example  A job requires: Lifting for 8 minutes Light work for 7 minutes Lift rate for the 8 minutes is 10 lifts/min  The lift frequency F would be: (10 x 8)/15 = 5.33 lifts/minute

17. Lifting Duration – Short  Short: <1hour, followed by a recovery time equal to 1.2 times the work time (Rest time / Work time = 1.2).  To be classified as short-duration, a 45-minute lifting job must be followed by at least a 54- minute recovery period prior to initiating a subsequent lifting session.

18. Lifting Duration – Moderate  Moderate: > 1 hour < 2 hours, followed by a recovery period of at least.3 times the work (Rest time / Work time =.3).  If a worker continuously lifts for 2 hours, then a recovery period of at least 36 minutes would be required before initiating a subsequent lifting session. If the recovery time requirement is not met, and a subsequent lifting session is required, then the total work time must be added together. If the total work time exceeds 2 hours, then the job must be classified as a long-duration lifting task.

19. Lifting Duration – Long  Long: 2 to 8 hours, with standard breaks (morning, lunch, and afternoon).

20. Variables – Frequency Multiplier  The FM value depends upon the average number of lifts/min (F), the vertical location (V) of the hands at the origin, and the duration of continuous lifting. For lifting tasks with a frequency less than.2 lifts per minute, set the frequency equal to.2 lifts/minute. For infrequent lifting (i.e., F <.1 lift/minute), however, the recovery period will usually be sufficient to use the 1-hour duration category.

21. Variable – Coupling Component  An optimal handle design has.75 - 1.5 inches diameter, > 4.5 inches in length, 2 inches clearance, cylindrical shape, smooth, non-slip surface.  An optimal hand-hold cut- out has the following approximate characteristics: > 1.5 inch height, 4.5 inch length, semi-oval shape, > 2 inch (5 cm) clearance, smooth non-slip surface, > 0.25 inches container thickness (e.g., double thickness cardboard).

22. Variable – Coupling Component  An optimal container design has: < 16 inches frontal length, < 12 inches height, a smooth non-slip surface.  A worker should be capable of clamping the fingers at nearly 90 degrees under the container, such as required when lifting a cardboard box from the floor.

23. Variable – Coupling Component  A container is considered less than optimal if it has: A frontal length > 16” height > 12” rough or slippery surfaces, Sharp edges, asymmetric center of mass, unstable contents, requires the use of gloves. A loose object is considered bulky if the load cannot easily be balanced between the hand-grasps.  A worker should be able to comfortably wrap the hand around the object without causing excessive wrist deviations or awkward postures, and the grip should not require excessive force.

24. Variable – Coupling Multiplier  The coupling multiplier (CM) is determined from decision tree and a tabled value.

25. Tabled Values

26. Tabled Values (cont.)

28. Coupling Quality

30. 23” 15” 44# 23” 63” 30”

31. Manufacturing Punch Press 44 23 15634800<.2<1Fair

35. OriginDestination

36. .44.891.0.95.86.44.751.0.86 16.3 14.5 Computing RWLs The RWL for the origin and destination is computed because significant control is required. Significant control: Precision placement where the worker 1) re-grasps the near the destination, 2) momentarily holds object at destination, or 3) carefully positions load at destination.

37. Computing Lifting Index 16.3 44 14.5 2.7 3.0 LIs > 1 indicate increased risk of low back pain.

38. Redesign the Job  Bring load closer to the body – rotate it 90 degrees.  Lower destination height.  Reduce travel distance.  Eliminate significant control..44.891.0.95.86.44.751.0.86 16.3 14.5

39. 23” 15” 44# 23” 63” 30” The reel is 12” wide.

40. Modifications 1.0.891.0.90.86.83.751.0.90.86 35.1 24.6 35.1 44 24.6 1.3 1.8

41. NIOSH Equation Limits  The model DOES NOT apply when lifting or lowering: With one hand Over 8 hours While seated or kneeling In restricted work space Unstable objects Wheelbarrows or shovels With high speed motion With unreasonable foot to floor friction In unfavorable environments (66-79 degrees and 33 to 50% humidity)